JP2540584B2 - Second-order nonlinear optical material and nonlinear optical element using the same - Google Patents

Description

The present invention relates to a second-order nonlinear optical material and a nonlinear optical element using the same. More specifically, the present invention relates to a second-order nonlinear optical material made of a dithiol derivative crystal and a nonlinear optical element using the same.

<Problems to be Solved by Prior Art and Invention> The non-linear optical effect is a phenomenon in which, when light enters a medium, polarization proportional to the second-order or higher-order term of the electric field of the light occurs, A non-linear optical effect appears remarkably under a strong electric field such as light. This nonlinear optical effect enables generation of the second harmonic, Kerr effect, optical bistability, etc. Especially, the second-order nonlinear optical effect occurring in proportion to the square of the electric field of light is an optical wavelength conversion element or an optical modulation element. Since it can be applied to non-linear optical elements such as the above, which can be applied to elements that promise the development of the optoelectronics field, they have received much attention.

The materials that make up these devices are currently KH ₂ PO ₄
Only some inorganic materials such as are in practical use. However, the non-linear optical constants of these inorganic materials are small, and therefore extremely high voltage or extremely high light intensity is required for the operation of the device. Therefore, the demand for materials having large nonlinear optical constants is extremely strong, and various materials have been searched for. In inorganic materials, lithium niobate (Li
NbO ₃ ) has the largest non-linear optical constant, but lithium niobate still has the drawbacks that it partially changes its refractive index when irradiated with intense laser light and is easily damaged by light. It has not been put to practical use.

Recently, it has been found that organic materials have much higher nonlinear optical properties than inorganic materials, such as 2-methyl-4-nitroaniline (MNA).
As typified by, a material having a π-electron system, an electron-donating group and an electron-withdrawing group in the molecule, and an extremely large nonlinear optical constant is drawing attention. But,
When a nonlinear optical element using such an organic nonlinear optical material is used as a light wavelength conversion element, particularly as a second harmonic generation element, the wavelength of the second harmonic is half the wavelength of the incident light, In order to make the device usable in a wide wavelength range, it is necessary for the device to have a wide transparent region, and it is preferable that the electronic transition absorption band is on the short wavelength side. However, in the conventional molecular design, the secondary state in the molecular state is used. Molecular nonlinear optical constant β of
In order to increase (hereinafter referred to as nonlinear optical constant β), the π-electron system in the molecule must be increased, which has a drawback that the electronic transition absorption band moves to the long wavelength side.
For this reason, the substitution of benzene ring with pyridine ring, pyrimidine ring, thiazole ring, etc. was also studied, but there is no known material that does not show absorption in the visible region and has a large nonlinear optical constant β. No element having the following non-linear optical effect, particularly, an excellent effect as an optical wavelength conversion element has been obtained.

<Objective> The present invention has been made in view of the above problems, and has a high nonlinear optical effect without absorption in the visible region.
It is an object to provide the following organic nonlinear optical material and a secondary nonlinear optical element using the same.

<Means and Actions for Solving Problems> The secondary nonlinear optical material of the present invention has the following general formula [I].
It is characterized by containing at least a compound represented by.

[In the formula, R ¹ , R ² , R ³ and R ⁴ each represent an organic substituent. However, at least one of R ¹ , R ² , R ³ and R ⁴ is an electron-withdrawing group. In the organic nonlinear optical material, in order to increase the nonlinear optical constant β, it is necessary that the electron transfer in the molecule smoothly progresses when polarization occurs due to the electric field of light. The compound of general formula [I] has an electron-donating sulfur atom, and at least one of R ¹ , R ² , R ³ and R ⁴ is an electron-withdrawing group, The compound of general formula [I] has a large nonlinear optical constant β.
And has a large nonlinear optical effect. Further, since the compound of the general formula [I] has a small π electron system in the molecule and has an electronic transition absorption band on the short wavelength side, it can be used in a wide wavelength range.

Further, the non-linear optical element of the present invention is characterized in that a second-order non-linear optical material containing at least the compound represented by the general formula [I] is used in the optical waveguide section.

According to the non-linear optical element, since the non-linear optical material is used in the optical waveguide section, a non-linear optical element having a large non-linear optical effect can be obtained, and high-intensity second harmonics can be generated even with laser light having low light intensity. It can be separated, and the electro-optical effect can be efficiently expressed even with a small voltage change.

The second-order nonlinear optical material will be described in detail below.

In the above general formula [I], R ¹ , R ² , R ³ and R ⁴ are organic substituents, and at least one of them is an electron withdrawing group. Examples of the organic substituent include a hydrogen atom; an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, pentyl, hexyl and octyl; methoxy, ethoxy, propoxy, isopropoxy, butoxy. , An alkoxy group such as tertiary butoxy, pentyloxy, hexyloxy; an acyl group such as formyl, acetyl, propionyl, butyryl, pentanoyl, hexanoyl, octanoyl, benzoyl; carbamoyl, methylcarbamoyl, dimethylcarbamoyl, ethylcarbamoyl, propylcarbamoyl, A carbamoyl group which may have a substituent such as hexylcarbamoyl, laurylcarbamoyl, benzylcarbamoyl, phenylcarbamoyl; amino,
An amino group which may have an alkyl group such as methylamino, dimethylamino, ethylamino, dimethylamino, propylamino, butylamino, hexylamino and octylamino; benzylamino, benzhydryl, tritylamino, phenylamino, diphenylamino Aralkylamino or arylamino groups such as; carboxy groups; methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, tertiary butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl, heptyloxycarbonyl, Octyloxycarbonyl, nonyloxycarbonyl, decyloxycarbonyl, undecyloxycarbonyl, dodecyloxycarbonyl, It may have a substituent such as alkoxycarbonyl group which may contain asymmetric carbon such as lidecyloxycarbonyl, tetradecyloxycarbonyl or pentadecyloxycarbonyl, phenoxylcarbonyl or p-nitrophenyloxycarbonyl. Aryloxycarbonyl, benzyloxycarbonyl,
Esterified carboxy groups such as aralkyloxycarbonyl such as benzhydryloxycarbonyl; halogen atoms such as methanesulfonyl, ethanesulfonyl, propanesulfonyl, butanesulfonyl, trifluoromethanesulfonyl, 2,2,2-trifluoroethanesulfonyl, etc. Alkanesulfonyl group which may have; acylamino group such as formamide, acetamide, propionamide, butyrylamino, hexanoylamino, benzoylamino; mercapto group; alkylthio group such as methylthio, ethylthio, propylthio, butylthio, octylthio; benzylthio, phenylthio , An aralkylthio or arylthio group which may have a substituent such as p-phenylthio; a hydroxyl group; a cyano group; a nitro group; a nitroso group; a sulfo group; Phenoxysulfonyl which may have a substituent such as alkoxysulfonyl such as cysulfonyl, ethoxysulfonyl, propoxysulfonyl, butoxysulfonyl, pentyloxysulfonyl, hexyloxysulfonyl and octyloxysulfonyl, phenoxysulfonyl and p-cyanophenoxysulfonyl. An esterified sulfo group of: sulfamoyl, methylsulfamoyl, ethylsulfamoyl,
Sulfamoyl group which may have a substituent such as phenylsulfamoyl and benzylsulfamoyl; quaternary ammonium group such as tetramethylammonio and ethyltrimethylammonio; sulfino group; chloro, bromo,
A halogen group such as fluoro or iodo; a group represented by the general formula — (CH ₂ ) _n —OH (n is a natural number) such as methylol, 2-hydroxyethyl, and 3-hydroxypropyl; an organic substituent such as a thiocarboxy group It can be illustrated. These organic substituents are preferably hydrogen-bondable substituents, and when the substituents are large, the crystallinity is poor and it becomes difficult to form an element. Therefore, the compact substituents are preferable.

In order to increase the nonlinear optical constant β, it is necessary for electrons to move smoothly when polarization occurs due to the electric field of light, and at least one of R ¹ , R ² , R ³ and R ⁴ is electron attracting. It is a sexual group. Examples of the electron-withdrawing group include a nitro group, a cyano group, a sulfonyl group optionally having a halogen atom, an acyl group, a carboxy group, an esterified carboxy group, and a carbamoyl optionally having a substituent. Various groups such as a group, a sulfo group, an esterified sulfo group, and a sulfamoyl group which may have a substituent can be selected, but in order to prevent the electron transition absorption band from being shown in the visible region, Hammett's An electron-withdrawing group having a substituent constant (σ _para ) of 0.7 or less is preferable. In the case of an electron-withdrawing group having a Hammett's substituent constant (σ _para ) of more than 0.7, the energy difference between the ground state and the excited state may be small, and the electronic transition absorption band may shift to a long wavelength (GBBarl
in and DDPerrin, Quart., Rev., 20 , 75,1966; LMYaqup
olskii and LZGandelsman, J., Gen., Chem., USSR, 3
5 , 1259, 1965 etc.). In particular, in order to make the intramolecular electron transfer proceed smoothly, among R ¹ , R ² , R ³ and R ⁴ , R ¹
It is preferable that at least one of R and R ² is an electron-withdrawing group, further R ^{1 and} R ² are different groups from the viewpoint of the molecular arrangement of the crystal, and particularly preferably R ¹ and R ² are respectively It is preferably a cyano group and an esterified carboxy group.

R ³ and R ⁴ can be appropriately selected from the organic substituents exemplified above, but a group selected from a hydrogen atom and an alkyl group is preferable.

Particularly, in the compound of the general formula [I], R ¹ is a cyano group, R ² is an alkoxycarbonyl group having 1 to 20 carbon atoms, particularly 1 to 6 carbon atoms, and R ³ is a hydrogen atom or methyl. A compound in which R ⁴ is a hydrogen atom or a methyl group has a large nonlinear optical constant β and is preferable.

The compound represented by the above general formula [I] can be synthesized by various methods. For example, the compounds of Examples 1 and 2 described below can be used.
It can be manufactured by the method as shown in.

The organic nonlinear optical material containing at least the compound represented by the general formula [I] may be a single component crystal of the compound represented by the general formula [I]. It may be a mixed crystal or a mixed solid composed of a mixture of a compound with another nonlinear optical material, a polymer having a substituent capable of hydrogen bonding or a liquid crystalline polymer. In addition,
When the compound represented by the general formula [I] and other non-linear optical materials are required not to exhibit absorption in the visible region, the characteristics of the compound represented by the general formula [I] are not impaired. In the range, when the absorption may be shown in the visible region, it is mixed in an appropriate range.

The single-component crystal of the compound represented by the general formula [I] does not exhibit absorption in the visible region, has a large nonlinear optical constant β even in a crystalline state, and has a remarkable second-order nonlinear optical effect.
Further, in the above-mentioned mixed crystal or mixed solid, the molecular arrangement in the crystal can be controlled to be an organic nonlinear optical material having a large second-order nonlinear optical effect.

As the other non-linear optical material, various organic non-linear optical materials are used, but a material having a large non-linear optical constant, for example, a second-order non-linear optical constant β of 5 × 10 5 is used.
-Compounds of ^-30 esu or more are used. As such an organic nonlinear optical material, a compound having an electron-withdrawing group and an electron-donating group in the molecule, for example, MNA, 1-methoxy-4- (2-nitrobenzylideneamino) benzene, 1-methoxy-4- (2-nitrobenzylideneamino) benzene, Ethoxy-4- (2-nitrobenzylideneamino) benzene, 1-propoxy-4- (2-nitrobenzylideneamino) benzene, 1-butoxy-4- (2-
Nitrobenzylideneamino) benzene, 1-hexyloxy-4- (2-nitrobenzylideneamino) benzene, 1-methoxy-4- (3-nitrobenzylideneamino) benzene, 1-ethoxy-4- (3-nitrobenzylideneamino) Benzene, 1-propoxy-4- (3-
Nitrobenzylideneamino) benzene, 1-butoxy-
4- (3-nitrobenzylideneamino) benzene, 1-
Hexyloxy-4- (3-nitrobenzylideneamino) benzene, 1-methoxy-4- (4-nitrobenzylideneamino) benzene, 1-ethoxy-4- (4-nitrobenzylideneamino) benzene, 1-propoxy-
4- (4-nitrobenzylideneamino) benzene, 1-
Butoxy-4- (4-nitrobenzylideneamino) benzene, 1-pentyloxy-4- (4-nitrobenzylideneamino) benzene, 1-hexyloxy-4- (4
-Nitrobenzylideneamino) benzene, 1-octyloxy-4- (4-nitrobenzylideneamino) benzene, 1-nonyloxy-4- (4-nitrobenzylideneamino) benzene, 1-methyl-4- (4-nitrobenzylideneamino) ) Benzene, 1-ethyl-4- (4-nitrobenzylideneamino) benzene, 1-propyl-4
-(4-Nitrobenzylideneamino) benzene, 1-butyl-4- (4-nitrobenzylideneamino) benzene, 1- (4-nitrobenzylideneamino) -4-hexylbenzene, 1- (4-nitrobenzylideneamino)
Schiff base type compounds such as -4-octylbenzene and 1-ethyl-4- (4-cyanobenzylideneamino) benzene; 1-methylaminoanthraquinone, 2-methylamineanthraquinone, 1,4-diamino-6-ethoxycarbonylanthraquinone Anthraquinone derivatives such as 1,4-diamino-2- (1-pyrrolidinyl) anthraquinone;
β, β-dicyano-4-methoxystyrene, β, β-dicyano-4-methylstyrene, 4-dimethylamino-
Styrene derivatives such as β, β-dicyanostyrene; 2-bromo-4-nitro-N, N-dimethylaniline; 4-N, N-dimethylamino-4′-nitrostilbene; 2-ethylamino-1,3, 4-thiadiazole; 4- (4'-dimethylaminoanilino) -2,5,6-trifluoro-1,3-dicyanobenzene, 4- (4'-methoxythiophenoxy) -2,5,6
-Trifluoro-1,3-dicyanobenzene and other benzene derivatives; 3,5-dimethyl-2 ', 4'-dinitro-1,1'-
Biphenyl-4-ol, 3,5-di-tert-butyl-
Examples include biphenyl derivatives such as 2 ', 4'-dinitro-1,1'-biphenyl-4-ol; 3-aminopyridine and the like. The mixing ratio of the compound represented by the general formula [I] and the above organic nonlinear optical material can be appropriately selected depending on desired optical characteristics, physical properties of the compound (eg, melting point, solubility, λmax, etc.).

The single crystal of the compound represented by the general formula [I] or the mixed crystal of the compound represented by the general formula [I] and the other non-linear optical material can be prepared by, for example, vacuum vapor deposition, molecular beam epitaxy or the like. Vapor growth method; Liquid phase growth method of evaporating the solvent of the solution containing the compound represented by the general formula [I], lowering the temperature, or precipitating crystals from a supersaturated solution; Crystals can be prepared by melting the compound shown and bringing it into contact with seed crystals and then pulling it up, or by a melt solidification method in which the melt is crystallized in a heating furnace having a temperature gradient. The organic solvent used in the liquid phase growth method may be a polar solvent such as methanol or ethanol having a hydroxy group capable of hydrogen bonding, a polar solvent such as acetonitrile, ethyl acetate, diethyl ether or tetrahydrofuran, benzene or toluene. It may be a nonpolar solvent or a small polar solvent such as cyclohexane. At this time, if necessary, crystals may be obtained from a solvent having an asymmetric carbon, for example, a solvent having an asymmetric carbon such as (R) -2-butanol.

The polymer having a hydrogen bondable substituent is a polymer having a hydrogen bondable group such as a hydroxy group, a carbonyl group, a carboxy group and an ether group, for example, polyvinyl alcohol, polymethyl methacrylate, polyacrylate. Examples of the acrylic resin include polyalkylene oxides such as polyethylene oxide.

Examples of the liquid crystal polymer include a side chain type liquid crystal polymer having a mesogen group in a side chain, a side chain type polyacrylate liquid crystal polymer, and a side chain type polysiloxane type liquid crystal polymer.

The polymer having a hydrogen bondable substituent or a mixture of the liquid crystal polymer and the above solid is used to utilize the molecular orientation of the polymer having a hydrogen bondable substituent and the liquid crystal polymer. The molecular arrangement of the compound represented by formula [I] can be controlled. In addition, among the compounds represented by the above general formula [I], compounds having an alkyl moiety, particularly a compound in which R ² is an alkoxycarbonyl group having 1 to 20 carbon atoms in the alkoxy moiety have compatibility with the above polymer. Since it is excellent, it is possible to further control the molecular arrangement of the compound represented by the general formula [I] in the solid mixture.

In addition, a solid mixture of the compound represented by the above general formula [I] and a polymer having a substituent capable of hydrogen bonding or a liquid crystalline polymer has a liquid crystallinity similar to that of the compound represented by the general formula [I]. It can be obtained by melting a mixture with a polymer or the like, then gradually cooling it to a liquid crystal state or the like, then applying an electric field, and then cooling and solidifying in that state. When the electric field is applied, the polymer having a substituent capable of hydrogen bonding and the liquid crystalline polymer solidify in an oriented state, so that the compound represented by the general formula [I] is obtained as a solid having a molecular alignment state without a symmetry center. be able to. In a mixture of the compound represented by the above general formula [I] and a polymer having a substituent capable of hydrogen bonding or a liquid crystalline polymer, the mixing ratio of each component is the compound represented by the general formula [I]. Is not particularly limited as long as it is capable of forming a molecularly oriented solid state, and the properties of the compound represented by the general formula [I] and the polymer having a hydrogen-bondable substituent and the liquid crystalline polymer ( For example, the phase transition temperature and the like) can be appropriately selected, and the content of the compound represented by the general formula [I] is usually about 2 to 60% by weight.

As described above, the organic nonlinear optical material containing at least the compound represented by the general formula [I] has a large nonlinear optical constant β and has a remarkable nonlinear optical effect. Therefore, the second-order nonlinear optical material of the present invention is a material for various forms of nonlinear optical elements used in the field of optoelectronics, for example, an optical wavelength conversion element, an optical modulation element such as a phase modulation element or an amplitude modulation element. It is suitable as a material. In particular, since the secondary nonlinear optical material containing at least the compound represented by the general formula [I], especially the single crystal of the compound represented by the general formula [I] does not exhibit maximum absorption in the long wavelength region, It is preferably used as a material for a conversion element.

The non-linear optical element of the present invention using the above-mentioned organic non-linear optical material will be described in detail below with reference to the accompanying drawings.

FIG. 1 is an example of a quadratic nonlinear optical element of the present invention, showing a schematic view of an optical waveguide type optical wavelength conversion element as an optical wavelength conversion element, which is represented by the general formula [I]. The core (1) made of an organic nonlinear optical material (hereinafter, referred to as a nonlinear medium) containing at least a compound having the nonlinear optical effect of (1) is a medium such as glass (hereinafter, isotropic) that does not show the second-order nonlinear optical effect. The structure is covered with a clad (2) composed of a medium), and in the figure, the alternate long and short dash line indicates the fundamental wave of the incident light and the alternate long and two short dashes line indicates the second harmonic. Light such as laser light is condensed by a lens or the like and is incident on the core (1) from one end surface of the light wavelength conversion element. Since the nonlinear medium forming the core (1) exhibits a large second-order nonlinear optical effect, the light emitted from the other end surface of the core (1) includes a fundamental wave and a second harmonic wave, and has a spectrum such as a prism or a filter. The second harmonic is extracted by separating by means.

2 and 3 are schematic diagrams showing other examples of the light wavelength conversion element, and in the drawings, the alternate long and short dash line and the alternate long and two short dashes line have the same meanings as in FIG. 1, respectively.

In the optical wavelength conversion element shown in FIG. 2, an optical waveguide section (2) made of a nonlinear medium is formed on a substrate (22) made of an isotropic medium.
1) is formed, and in the optical wavelength conversion element shown in FIG. 3, a substrate (32) made of an isotropic medium,
An optical waveguide section (31) made of a non-linear medium is formed between it and a top layer (33) also made of an isotropic medium. The light wavelength conversion element described above is used in the same manner as the light wavelength conversion element shown in FIG.

Further, as the light modulation element, a device of a form conventionally used can be used. FIG. 4 shows, as an example thereof, a schematic view of an optical waveguide type optical modulation element operating in the horizontal direction, in which a substrate (42) made of an isotropic medium is provided with an optical waveguide section (41) made of a nonlinear medium. In addition, two electrodes (43) are provided at positions facing each other along the length direction via the optical waveguide (41), and an electric field is generated by applying a voltage between the electrodes (43). Is formed. In the above element, when the light incident from one end of the optical waveguide section (41) in the length direction passes through the optical waveguide section (41) and is emitted from the other end surface, a non-linear medium forming the optical waveguide section (41). When the refractive index of the light changes, the phase of the emitted light also changes. Since the refractive index of the non-linear medium changes depending on the applied voltage, the phase of the emitted light can be modulated by changing the applied voltage between the electrodes (43).

The second-order nonlinear optical element of the present invention is not limited to the above example, and various forms are possible.
As the optical wavelength conversion element, a single non-linear medium can be used as the element, and as in the above example, an optical waveguide made of a non-linear medium is formed on a substrate made of an isotropic medium and the second harmonic wave is taken. You can also use a configuration such as [J.Zyss, J.Molea
ular Electronics 1 , 25 (1985), etc.] In addition, the optical modulator may be a vertical operation optical waveguide type optical modulator capable of amplitude modulation, or a voltage is directly applied to the crystal itself. You can also In the light modulation element, the electric field application direction for efficiently performing the phase modulation differs depending on the symmetry of the nonlinear medium, the direction of the crystal axis, and the like. Therefore, it is preferable to appropriately change the electrode configuration based on these. In addition, since the light is confined in the waveguide by using the waveguide type optical wavelength conversion element, the optical power density is increased and the interaction length can be increased, so that the efficiency can be improved, Furthermore, phase matching using modal dispersion is also possible.

The element can be manufactured by various methods. In the optical wavelength conversion element shown in FIGS. 1 to 4, the core (1) and the optical waveguides (21) (31) are used.
The formation of (41) is performed, for example, by heating and melting the non-linear medium raw material in a capillary made of an isotropic medium, on the same waveguide substrate made of an isotropic medium, or between waveguide substrates made of an isotropic medium. After that, it is performed by a method of depositing crystals by slowly cooling, a method of depositing crystals on the substrate by a vacuum deposition method, a high frequency sputtering method, or the like,
Alternatively, a method of precipitating crystals from the solution in which the non-linear medium raw material is dissolved in an appropriate organic solvent in the above-mentioned capillary, on the substrate or between the substrates may be used. Further, in some cases, after the portion of the capillary, on or between the substrates, which should be the contact interface with the nonlinear medium is treated with an alignment treatment agent, the nonlinear medium is precipitated and crystal-grown to form an optical wavelength conversion element or the like. May be. As the alignment treatment agent, an inorganic salt and an organic salt (for example, hexadecyltrimethylammonium bromide), a thin film made of a suitable polymer (for example, polyamide), a metal complex, a metal thin film (for example, an obliquely evaporated metal film) Etc.) are exemplified.

<Example> Hereinafter, the present invention will be described in detail based on an example.

Example 1 Chloroacetaldehyde (10 mmol) was added to a mixture of ethyl 2-cyano-3,3-dimercaptoacrylic acid disodium salt (10 mmol), potassium dihydrogen phosphate (10 mmol) and water (50 ml). Add and stir. After cooling sufficiently, the colorless precipitate that precipitates was collected by filtration, and the obtained crystals were recrystallized with a mixed solvent of toluene-heptane (1: 1). Then, 520 mg of the thus obtained crystal was 1
After dissolving in 0 ml concentrated sulfuric acid, pour into ice water. The precipitated precipitate was collected by filtration, dried and purified by silica gel column chromatography to give white ethyl 1,3-dithiol-
315 mg of 2-ylidene cyanoacetate was obtained. When the ultraviolet-visible absorption of the obtained crystal in a methanol solution was measured, the maximum absorption wavelength was 368 nm.

Melting point: 178-179 ° C. Also, the nuclear magnetic resonance spectrum (JEOL) of the compound of Example 1
Using JNM-PMX60 NMR SPECTROMETER. The same shall apply hereinafter) and infrared absorption spectrum (HITACHI 270-30 IR SPECTROPHOT
Using OMETER, KBr method. The same shall apply hereinafter). ¹ H-NMR (DMSO-d ₆ ) δ: 1.37 (3H, t), 4.30 (2H, q) 7.50 (2H, s) IR (cm ^-1 ): 2220, 1680 [Second-order nonlinear optical effect of crystals] ] The compound obtained in Example 1 above was ground in a mortar and sandwiched between two pieces of prepared glass, and 1.06 μm light (100 m of YAG laser (Quauta-Ray, DCR-2)) was used.
When the sample powder was irradiated with (J / 8 ns pulse), scattered light of the second harmonic (0.53 μm) was visually observed, and it was found that this compound had a second-order nonlinear optical effect. Further, the second harmonic intensity thereof was extremely stronger than that of urea.

[Evaluation of β] The electronic state of the compound obtained in the above-mentioned Example 1 was analyzed by Parise
r-Parr-Pople (PPP) method [eg A. Martin, Acta. Chimi
ca Academiae Scientiarum Hungaricae, 84 , 259, (197
5)], and based on this, the nonlinear optical constant β in the molecular state represented by the formula below was calculated to be 20 × 10 ^-30 esu (at 1.06 μm) [JL
Oudar, J., Chem., Phys., 67 , 446 (1977)].

[E: electron charge, (H is Planck's constant), m: electron mass, w: energy difference between ground state and excited state, f: oscillator strength, Δμ _ge : difference in permanent polar moment between ground state and excited state] In addition, β obtained by the PPP method of MNA and 4-N, N-dimethylamino-4′-nitrostilbene (DANS) The values of are shown in the table below. The values obtained are from JLOudar et al. [JLOudar,
J., Chem., Phys., 67 , 446 (1977)], based on the measured value, it agrees very well with the literature value calculated using the equation for calculating the nonlinear optical constant β, and the PPP method The validity of calculating the nonlinear optical constant β using is shown. Therefore, the nonlinear optical constants β of the compounds obtained in the above examples
Is larger than the MNA.

Example 2 2-Cyano-3,3-dimethylcaptoacrylic acid ethyl disodium salt (10 mmol) and ethanol (40
Methyl propargyl bromide (10 mmol) was added to the mixture (1 ml) and the mixture was stirred at room temperature for 1 hour, and then water (60 ml) was added. Then, after acidifying the reaction solution with hydrochloric acid, the deposited precipitate was collected by filtration and dried to obtain ethyl 4-methyl-1,3
-1.35 g of dithiol-2-ylidene cyanoacetate was obtained. This was recrystallized from a mixed solvent of heptane and water-methanol to obtain white crystals. The maximum absorption wavelength of this product in a methanol solution was 373 nm.

Melting point: 131-133 ° C. When the second-order nonlinear optical effect of the crystal obtained above was measured in the same manner as in the method of Example 1, strong second harmonic generation was observed.

Example 3 In the same manner as in Example 2, using appropriate starting materials, ethyl 4,5-dimethyl-1,3-dithiol-2-ylidene cyanoacetate was obtained. The maximum absorption wavelength of this product in a methanol solution was 378 nm.

Melting point: 140 to 141 ° C ¹ H-NMR (CDCl ₃ ) δ: 1.37 (3H, t), 2.23 (6H, s) 4.30 (2H, q) IR (cm ^-1 ): 2210, 1680 Obtained as above When the second-order nonlinear optical effect of the crystal was measured in the same manner as in the method of Example 1, generation of a strong second harmonic 22 times that of urea was observed.

In addition, as a result of X-ray structural analysis, the crystal structure of the compound of Example 3 was a triclinic system and space group P1, and it was found that the molecules are arranged in such a state that their mutual dipole moments are not canceled at all. did.

Example 4 In the same manner as in Example 1, methyl 1,3-dithiol-2-ylidene cyanoacetate was obtained using an appropriate starting material. The maximum absorption wavelength of this product in a methanol solution was 368 nm.

Melting point: 204-205 ° C. When the second-order nonlinear optical effect of the crystal obtained above was measured by the same method as in Example 1, strong second harmonic generation was observed.

Example 5 In the same manner as in Example 2, propyl 4-methyl-1,3-dithiol-2-ylidene cyanoacetate was obtained using an appropriate starting material. The maximum absorption wavelength of this product in a methanol solution was 378 nm.

Melting point: 82-83 ° C ¹ H-NMR (CDCl ₃ ) δ: 1.00 (3H, t), 1.77 (2H, m) 2.38 (3H, s), 4.20 (2H, t) 6.63 (1H, s) IR ( cm ⁻¹ ): 2220, 1690 When the second-order nonlinear optical effect of the crystal obtained above was measured in the same manner as in Example 1, strong second harmonic generation was observed.

Example 6 In the same manner as in Example 2, using appropriate starting materials, isopropyl 4-methyl-1,3-dithiol-2-ylidene cyanoacetate was obtained. The maximum absorption wavelength of this product in a methanol solution was 378 nm.

Melting point: 116 to 117 ° C. When the second-order nonlinear optical effect of the crystal obtained above was measured in the same manner as in the method of Example 1, strong second harmonic generation was observed.

[Formation of Light Wavelength Converting Element and Test Results] Example 7 A Pyrex glass tube was worked with an oxygen burner to obtain a glass capillary having an inner diameter of about 3 μm. Example 1 above
Melt the sample obtained by ~ 6, and inject the solution into the capillary by capillarity. Further, when the capillary was pulled out from the furnace using a Bridgman furnace having a melting point plus 5 ° C., a single crystal region of about 5 mm was obtained. This single crystal region was cut out with a file and a YAG laser (1.06 μm) light was made incident on the single crystal in the glass capillary using a 20 × objective lens. As a result, green (0.
The second harmonic (532 μm) was radiated from the end face of the capillary.

Example 8 A glass capillary was obtained in the same manner as in Example 7 above. In addition, the samples obtained in Examples 1 to 6 were heated to the boiling point of ethanol, which is an alcohol solvent, and dissolved to obtain a saturated solution. While keeping this solution at a temperature near the boiling point of the solvent, attach one end of the glass capillary heated to about the same temperature as the above to the above solution, inject the solution using the capillary phenomenon, and then heat and seal both ends of the glass capillary. It was

Using a Bridgman furnace, the capillary was pulled out from the furnace by the method of cooling from the lower end at the boiling point of the solvent, and an end crystal region of 5 to 30 mm was obtained. After cutting out this edge crystal region and polishing the end surface, YAG laser (1.06 μm) light was made incident from one end surface of the single crystal in the glass capillary using a 20 × objective lens. As a result, the second harmonic of green (0.532 μm) was radiated from the end face of the capillary.

Example 9 The samples obtained in Examples 1 to 6 were heated and melted and injected into the glass capillaries obtained in the same manner as in Example 7 as in Example 7. Each glass capillary was placed in a Bridgman furnace heated above the melting point of each sample. When pulling out the glass capillary, attach a single crystal of each sample grown from an alcoholic solvent to the cooled end face of the glass capillary, pull out the glass capillary from the furnace so that the single crystal does not dissolve, and Single crystal regions of 1 to 30 mm each were obtained in the glass capillary.

This single crystal region was cut out and YA was prepared in the same manner as in Example 7.
When G laser (1.06 μm) light was made incident from one end face of the crystal in each glass capillary, it was observed that the second harmonic of green (0.532 μm) was generated from the other end face of each glass capillary.

<Advantages of the Invention> As described above, according to the second-order nonlinear optical material of the present invention, the compound represented by the general formula [I] has an electron-withdrawing property in a ring containing an electron-donating sulfur atom. Since the substituents are bonded, electron transfer rapidly occurs when polarization is caused by an electric field such as light, the nonlinear optical constant β is large, and a remarkable nonlinear optical effect is exhibited.

Further, according to the nonlinear optical element of the present invention, since the second-order nonlinear optical material is used in the optical waveguide section, a second-order nonlinear optical element can be obtained, and the second-order nonlinear optical element with high intensity is obtained even with weak laser light. It has a unique effect that the second harmonic can be decomposed and the electro-optical effect can be efficiently expressed even with a small voltage change.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical wavelength conversion element as an example of a second-order nonlinear optical element of the present invention, and FIGS. 2 and 3 are optical wavelength conversion elements as other examples of nonlinear optical elements, respectively. Schematic diagram, FIG. 4 shows a schematic diagram of a light modulation element as another example. (1) …… Core, (2) …… Clad (21) (31) (41) …… Optical waveguide, (22) (32) (42) …… Substrate (33) …… Top layer, (43 )……electrode.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Shimizu 1-3-1, Shimaya, Konohana-ku, Osaka City, Osaka Prefecture Sumitomo Electric Industries, Ltd. Osaka Works (72) Yutaka Shibata, Shimaya, Konohana-ku, Osaka City, Osaka Prefecture 1 to 3 Sumitomo Electric Industries, Ltd. Osaka Works

Claims (11)

(57) [Claims] 1. A general formula [I] [In the formula, R ¹ , R ² , R ³ and R ⁴ each represent an organic substituent. However, at least one of R ¹ , R ² , R ³ and R ⁴ is an electron-withdrawing group. ] A second-order nonlinear optical material comprising at least a compound represented by 2. The second-order nonlinear optical material according to claim 1, wherein in the compound of the general formula [I], the Hammett's substituent constant (σ _para ) of the electron-withdrawing group is 0.7 or less. 3. In the compound of general formula [I], R ¹ and
The second-order nonlinear optical material according to claim 1, wherein at least one of R ² is an electron-withdrawing group. 4. The second-order nonlinear optical material according to claim 3, wherein R ¹ in the compound of general formula [I] is a cyano group. 5. The second-order nonlinear optical material according to claim 3, wherein R ² in the compound of general formula [I] is an esterified carboxy group. 6. The secondary nonlinear optical material according to claim 1, wherein R ³ in the compound of the general formula [I] is a hydrogen atom or an alkyl group. 7. The second-order nonlinear optical material according to claim 1, wherein R ⁴ in the compound of general formula [I] is a hydrogen atom or an alkyl group. 8. In the compound of general formula [I], R ¹ is a cyano group, R ² is an alkoxycarbonyl group having 1 to 20 carbon atoms in the alkoxy moiety, and R ³ is a hydrogen atom or a methyl group. , R ⁴ is a hydrogen atom or a methyl group.
The described second-order nonlinear optical material. 9. A quadratic nonlinear optical material according to claim 1, which is composed of a single crystal of the compound of the general formula [I]. 10. A non-linear optical element, wherein the second-order non-linear optical material according to claim 1 is used in an optical waveguide section. 11. The nonlinear optical element according to claim 10, wherein the nonlinear optical element is a light wavelength conversion element.